I had something similar with my temp control slider (it sounds like you have a non AC car?); the cable was binding. Pulled out the HVAC control, found what it was binding on and that was that. Compared to a lot of cars, removing even large chunks of the interior is not hard. Once you get eyes on what's going on, it's no longer a guessing game.
------------------
-Chris
'85 V6 SE 4sp (SOLD)
'88 GT - Series 3 SC3800 w/ 3.5" pulley, 1.8" rockers, 3" exhaust, 3.5" intake, 3.29 gearing. Installed and tuned by Sinister Performance
'99 Kawasaki Vulcan 500, owned since new
'09 G37x Sedan w/ Premium & Nav (wife's car)
'13 G37xS Sedan (new daily driver)
'14 Yamaha FJR - 0-60 in 2.8s w/ 34MPG!!!